1. Field of the Invention
This invention pertains generally to network multicast communication, and more particularly to ordering services for tree-based concurrent multicasting.
2. Description of the Background Art
Multicast communication generalizes the unicast (point-to-point) and broadcast (one-to-all) communication models in computer networks to multipoint dissemination of messages. A source must send a packet only once to the network interface, and packets are transparently replicated on their transmission paths to the receivers. This form of communication is indispensable for networked applications with high-volume data transfer, such as distributed software updates, news casts, video-on-demand, or telecollaboration systems. The concept of multicasting is gradually adapted and deployed with IP multicast protocols in the Internet, however, those mechanisms lack reliable or order-preserving delivery of packets to a multicast group. Reliable multicast guarantees that all packets sent from a source to a group of receiving hosts are disseminated without error. Ordered delivery of multimedia data from multiple sources is essential for a growing number of Internet applications, with the goal to preserve data consistency and the coherency of group activities. Ordering in previously developed reliable multicasting protocols is only considered for nodes arranged in ring topologies, or deferred to the application layer. A large body of work in the field of total and causal ordering for multicast messages is centered around fault tolerance or consistency issues in distributed systems.
Therefore, a need exists for a method of ordered multicasting that operates directly on reliable multicast trees to provide increased scalability, efficiency, and practicality. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed multicast protocols.